Drug abuse by an individual during adolescence, a significant period of maturation, may enhance their vulnerability to the central nervous system (CNS) effects of abused drugs. The present application brings together a multidisciplinary team of investigators to examine whether pharmacodynamic changes resulting from the presence of ovarian hormones and chronic A9-THC administration alters the subjective effects of the drug, increases the vulnerability of females to drug abuse, and changes their ability to learn. Chronic exposure to A9-THG is of particular interest because this illicit drug is widely abused by adolescents, while the presence or absence of ovarian hormones is of interest as a cofactor because: 1) ovarian hormones may have independent or interactive influences on maturation and 2) published data generated by these investigators indicate that the ovarian hormone estrogen can attenuate the detrimental effects of A9- THC on learning in female rats and alter the binding of cannabinoid ligands in brain areas that are critical for learning such as the hippocampus. For these same reasons, and because there is a paucity of data regarding the effects of A9- THC using female models, all of the planned behavioral experiments will use female rats and involve the presence or absence of ovarian hormones in A9-THC-treated subjects. In addition, subjects in each behavioral group will be sacrificed to examine potential changes in cannabinoid receptors and endogenous cannabinoid levels in relevant brain areas. More specifically, the aims of this grant will determine whether: 1) peri-adolescent A9-THC administration in gonadally intact female rats will alter their sensitivity as adults to the acute behavioral effects of A9-THC when compared to either gonadally intact or ovariectomized females that were drug-naTve during adolescence; 2) peri-adolescent A9- THC administration in gonadally intact female rats will alter the pharmacodynamic response of the cannabinoid system to acute challenge with A9-THC as an adult when compared to either gonadally intact or ovariectomized females that were drug-naTve during adolescence; 3) A9-THC administration from adolescence to adulthood in gonadally intact female rats will produce effects on learning that are different from those produced in either gonadally intact or ovariectomized females whose chronic administration of A9-THC did not start until post adolescence; and 4) A9-THC administration from adolescence to adulthood in gonadally intact female rats will alter the endogenous response of the cannabinoid system when compared to either gonadally intact or ovariectomized females whose chronic administration of A9-THC did-not start until post adolescence.. Together, data from these experiments will demonstrate how drug abuse and hormonal status during adolescence may permanently alter brain function and the liability of subsequent abuse of A9-THC.